1. Field of the Invention
The present invention relates to a four-wheel drive vehicle which is capable of being switched over between a two-wheel drive state and a four-wheel drive state.
2. Description of the Related Art
The main type of the current four-wheel drive vehicles is a full-time type four-wheel drive vehicle including a front differential adapted to distribute a driving force between left and right front wheels, a center differential adapted to distribute the driving force between the front wheels and rear wheels, and a rear differential adapted to distribute the driving force between the left and right rear wheels. A part-time type four-wheel drive vehicle includes a clutch for intermittently transmitting the driving force to a transfer means adapted to transmit the driving force for the front wheels to the rear wheels.
To transmit the driving force to the left and right rear wheels, for example, when the vehicle runs out of a muddy place, the full-time type four-wheel drive vehicle is accompanied by a problem that it is necessary to mount a differential lock device on the center differential and the rear differential, resulting in an undesirabe increase in the number of parts and a complicated structure. The part-time type four-wheel drive vehicle is accompanied by a problem that because clutches are provided on the transfer means, the number of parts is increased, and the structure is complicated.